# Cat Lump With Pus: Abscess or Something Else? A cat lump with pus is most often an abscess from a bite or scratch, and it usually needs veterinary drainage plus antibiotics. The same appearance can also come from a ruptured cyst, an infected tumor, or a deeper infection that has spread. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - A pus-filled lump that appears suddenly after a cat fight is most likely an abscess, and it often needs to be opened and drained by a veterinarian. - Do not squeeze or lance the lump at home. You can spread infection deeper into tissue or into your own skin. - A lump that keeps refilling, does not heal in a few days, or returns in the same spot needs a closer look, because some tumors can look like infected cysts [1]. - Fever, not eating, hiding, limping, or a bad smell means call your vet today. - Trouble breathing, collapse, or a lump that bursts with a large amount of foul fluid means go to an emergency clinic now. ## What a Pus-Filled Lump Looks Like in Cats An abscess is a pocket of pus walled off under the skin. Early on it feels like a warm, firm, painful swelling. The cat may flinch when you touch it. As pressure builds, the skin over it thins, hair falls out, and the lump turns red or purple. Many abscesses eventually break open on their own and drain thick, bloody, foul-smelling fluid. Cats hide pain well, so the first clue is often behavior. Your cat may hide under the bed, stop eating, run a fever, or limp if the lump sits on a leg or near the tail base. A lump on the bum is common after bites near the tail, and it can be easy to miss under thick fur. Not every lump with pus is an abscess. Sebaceous gland adenomas, which are common benign skin tumors in cats, can become crusted and inflamed with pus [1]. That is one reason a lump that looks infected still deserves a hands-on exam. ## Main Causes of a Cat Lump With Pus The table below covers the most common possibilities. Urgency reflects how fast the problem can worsen, not how serious every case turns out to be. | Cause | Typical clues | How urgent | |---|---|---| | Bite-wound abscess | Sudden swelling after a fight, fever, pain, drains foul fluid, often on the tail base, cheek, or leg | Same-day vet visit | | Ruptured or infected cyst | Slow-growing lump that has been there a while, then becomes red and drains | Routine to same-day, depending on pain and fever | | Infected or ulcerated tumor | Lump that keeps returning, does not fully heal, or grows despite treatment [1] | Prompt exam, biopsy often needed | | Foreign body abscess | Chronic draining tract, sometimes after a plant awn or splinter, may not heal with antibiotics alone [2] | Same-day vet visit | | Lymph node abscess | Swelling near a scratch or bite site, may follow cat scratch disease [3] | Same-day vet visit | | Deep or internal abscess | Lethargy, breathing trouble, weight loss, or pain in the belly or chest [4][5] | Emergency | ### Bite-Wound Abscesses This is the classic cause. Cat teeth are thin and sharp, so a bite injects bacteria deep under the skin through a tiny hole that seals over within hours. Bacteria multiply in the closed pocket, and within a few days you have a hot, tender lump. Pasteurella multocida is a common culprit in cat bite and scratch infections [6]. ### Cysts and Benign Skin Tumors Sebaceous adenomas are common benign tumors in cats, and Persians are the breed most predisposed. They often appear in multiple spots, most often on the head, and they can be crusted and inflamed with pus [1]. These are not dangerous in themselves, but they can look alarming and may need to be distinguished from something worse. ### Tumors That Can Look Infected Some cancers present as lumps that ulcerate, drain, or bleed. Skin lymphoma can cause lumps, redness, flaking, or ulcers, especially near the lips and footpads, and it can spread quickly [7]. A sarcoma that develops at a previous injection site can return after surgery and invade nearby tissue [8]. The lesson is simple: a lump that keeps coming back in the same place is not just a stubborn abscess. ### Abscesses in Other Body Areas Abscesses can form inside the body, not only under the skin. A pancreatic abscess can cause weight loss, vomiting, and increased thirst, and it may persist despite months of antibiotics and repeated drainage [4]. An abscess in the chest can cause breathing difficulty and lethargy [5]. A liver abscess from a migrating grass awn has been reported in a cat, with cough, weight loss, and poor appetite [2]. An abscess near the ear can even spread to the brain, causing balance loss and seizures [9]. These are uncommon, but they explain why a cat that seems "just a bit off" with a lump still needs an exam. ## Red Flags That Mean Emergency Some signs mean you should stop reading and call an emergency clinic. - Open-mouth breathing, fast breathing, or blue gums - Collapse, weakness, or inability to stand - A lump that bursts and drains a large amount of foul fluid, especially with a sudden decline - Severe pain, crying, or a cat that will not let you near it - Swelling that spreads fast across a limb or the belly - Seizures, head tilt, circling, or sudden balance loss [9] - Not eating or drinking for more than 24 hours with a fever A ruptured abscess can release bacteria into the bloodstream, and deep infections can become life threatening. Prompt care matters. ## What You Can Safely Do at Home Home care is about comfort and hygiene, not treatment. The infection lives under the skin, so surface cleaning alone will not cure it. - Do not squeeze, poke, or cut the lump. You can push bacteria deeper and injure yourself. - Wear gloves if the lump is draining. Cat scratch disease is a zoonosis, meaning it can pass from cats to people, and it can cause swollen lymph nodes and abscesses in humans [3]. - Keep the area clean with a warm damp cloth, and pat dry. Do not scrub. - Use a clean towel or puppy pad under your cat's favorite bed, and wash bedding in hot water. - Keep your cat indoors and away from other cats until a vet sees the lump. - Offer food and water, and note whether your cat eats, drinks, urinates, and stools. - Do not give human pain medications. Many are toxic to cats. Your veterinarian will choose a safe pain plan based on your cat's weight and health. If the lump is small, soft, and your cat is eating and acting normal, a routine visit within a day or two is reasonable. If your cat is painful, feverish, or not eating, go sooner. For help sorting mild lumps from ones that need a visit, see [Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor](/knowledge/veterinary-medicine/vet-visit-decisions/cat-skin-bumps-lumps). ## What Your Veterinarian Will Check Your vet will start with a full physical exam, including a temperature, weight, and a careful feel of the lump and nearby lymph nodes. They will ask about outdoor access, fights, recent scratches, and how long the lump has been there. ### Tests Your Vet May Recommend - Fine needle aspirate: a thin needle collects cells or fluid from the lump. This is quick and often done in the exam room. - Cytology: the sample is examined under a microscope. In one pancreatic abscess case, cytology showed suppurative inflammation with bacterial infection [4]. - Bacterial culture and sensitivity: identifies the bacteria and which antibiotics will work. Pasteurella multocida has been cultured from abscesses in cats [4], and it is a common bite-wound organism [6]. - Blood work: checks for fever, anemia, organ changes, and underlying disease such as diabetes [4]. - Imaging: ultrasound or CT can find deep abscesses or foreign bodies that cannot be felt [5][2]. - Biopsy: a tissue sample is needed when a lump could be a tumor. Skin lymphoma is diagnosed by blood tests and biopsy of a lump or enlarged lymph node [7]. ### Treatment Basics Most superficial abscesses are treated by draining the pus, flushing the pocket, and starting antibiotics. Some need a drain left in place for a few days. Your veterinarian calculates the antibiotic dose from your cat's weight and health, so never reuse leftover medication from a previous illness. Deep abscesses may need surgery. A chest abscess in one cat required video-assisted thoracic surgery after medical management failed [5]. A brain abscess in another cat was treated with surgical drainage and antibiotics, and the cat recovered neurologically [9]. These are serious cases, but they show that aggressive treatment can work. If the lump is a tumor, treatment depends on the type. Skin lymphoma is often treated with multi-drug chemotherapy, and hair loss does not occur in cats as a chemotherapy side effect [7]. Some sarcomas need surgery plus radiation [8]. ## Prevention and Monitoring You cannot prevent every lump, but you can lower the odds and catch problems early. - Keep cats indoors or supervise outdoor time to reduce fights and bite wounds. - Spay and neuter your cats. Fighting over mates is a major cause of bite abscesses. - Check your cat's skin weekly. Run your hands over the body, including the tail base, armpits, and groin. A lump on the bum is easy to miss. - Photograph any lump with a ruler or coin next to it, and note the date. This helps your vet judge growth over time. - After any cat fight, clean small wounds and call your vet. Bite wounds seal fast and abscess days later. - If your cat has had a lump removed, keep follow-up appointments. Recurrence is a real risk with some tumors [1][8]. - Watch for subtle signs: hiding, grumpiness when picked up, or a change in grooming habits. If your cat has a draining ear or head-shaking along with a lump near the ear, see [Cat Ear Infection](/knowledge/veterinary-medicine/clinical-methods/cat-ear-infection). If the lump is on the skin and oozing pus with widespread redness, see [Cat Skin Rash with Pus: When to Rush to the Vet](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-skin-rash-with-pus-when-to-rush). ## Limitations and When to Contact a Veterinarian This article cannot tell you what your cat's lump is. Only an exam, and often a sample, can do that. Individual cases need a veterinarian who can see, feel, and test the lump. Call your veterinarian the same day if your cat has a painful lump, a fever, is not eating, is limping, or has a lump that is growing or draining. Go to an emergency clinic now if your cat is having trouble breathing, has collapsed, is having seizures, or has a lump that suddenly bursts with a large amount of foul fluid. Schedule a routine visit if you find a small, non-painful lump and your cat is otherwise normal, but do not wait weeks to see if it changes. ## Frequently Asked Questions ### Will a cat abscess go away on its own? Sometimes a superficial abscess will rupture and drain by itself, and the cat may improve for a while. The problem is that the pocket often refills, and the infection can spread deeper. Veterinary drainage and antibiotics give the best chance of full resolution. ### Can I pop my cat's abscess at home? No. Popping or lancing at home can push bacteria deeper, cause more pain, and expose you to infection. Cat scratch disease is a zoonosis that can cause swollen lymph nodes and abscesses in people, so handling draining pus without gloves is risky [3]. ### How do I know if a lump is a tumor and not an abscess? You usually cannot tell by looking. Tumors such as sebaceous adenomas can be crusted and inflamed with pus, and skin lymphoma can cause lumps and ulcers [1][7]. A fine needle aspirate or biopsy is the only reliable way to tell the difference. ### Why does my cat keep getting lumps in the same spot? A lump that returns in the same place may be an incompletely drained abscess, a foreign body that was never removed, or a tumor that was not fully excised. Recurrence is expected with some tumors even after surgery [1][8]. Your vet may recommend imaging or a biopsy. ### Is a lump on my cat's bum always an abscess? No. The tail base is a common site for bite-wound abscesses, but lumps there can also be cysts, tumors, or impacted anal glands. A lump on the bum is easy to miss under fur, so have your vet examine it instead of assuming it is a simple abscess. ## Related Articles - [Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor](/knowledge/veterinary-medicine/vet-visit-decisions/cat-skin-bumps-lumps) - [Cat Bite Abscess: Signs, Home Care, and When to See the Vet](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-bite-abscess-signs-home-care-when-to-see-vet) - [Cat Ear Infection](/knowledge/veterinary-medicine/clinical-methods/cat-ear-infection) - [Cat Skin Rash with Pus: When to Rush to the Vet](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-skin-rash-with-pus-when-to-rush) - [Ear Polyps in Cats: Signs, Diagnosis, Surgery, and Recurrence](/knowledge/veterinary-medicine/clinical-methods/ear-polyps-in-cats) - [Symptoms Of Cat Ear Infection](/knowledge/veterinary-medicine/symptom-guides/symptoms-of-cat-ear-infection) - [Cat Abscess: Home Care and When to See a Vet](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-abscess-care) - [Cat Cyst vs Abscess vs Cancer: Key Differences](/knowledge/veterinary-medicine/skin-allergy-and-ear-care/cat-cyst-vs-abscess-vs-cancer) - [Cat After a Fight: Wounds, Abscesses and When to See a Vet](/knowledge/veterinary-medicine/emergency-and-first-aid/cat-after-fight-wounds) - [Feline Bartonellosis: Clinical Manifestations and Diagnostic Challenges in Cats](/knowledge/bacteria/pet-bacteria/feline-bartonellosis-clinical-manifestations-diagnostic-challenges-cats) ## References 1. [Tumors of the Skin in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/skin-disorders-of-cats/tumors-of-the-skin-in-cats). Merck Veterinary Manual. 2. [Hepatic abscess caused by an inhaled migrating grass awn in a cat: first description and minimally invasive surgical approach](https://pubmed.ncbi.nlm.nih.gov/41727923/). JFMS open reports, 2026. 3. [Treatment-Resistant Femoral Lymph Node Abscess Caused by Cat Scratch Disease: A Case Confirmed by Polymerase Chain Reaction](https://pubmed.ncbi.nlm.nih.gov/41583232/). Cureus, 2025. 4. [Recurrent pancreatic abscesses coexisting with a suspected adenocarcinoma in a cat](https://pubmed.ncbi.nlm.nih.gov/42499990/). JFMS open reports, 2026. 5. [Video-assisted thoracic surgery of a caudal mediastinal paraoesophageal abscess in a cat with recurrent pyothorax](https://pubmed.ncbi.nlm.nih.gov/42146261/). JFMS open reports, 2026. 6. [Invasive Pasteurella multocida Infection With Cervical Abscess and Sternoclavicular Septic Arthritis Following a Cat Scratch in a Patient With Lymphedema: A Case Report](https://pubmed.ncbi.nlm.nih.gov/41404448/). Cureus, 2025. 7. [Immune System Tumors in Cats - Cat Owners](https://www.merckvetmanual.com/cat-owners/immune-disorders-of-cats/immune-system-tumors-in-cats). Merck Veterinary Manual. 8. [Suspected recurrent sarcoma resembling feline injection-site sarcoma with spinal cord invasion in a cat](https://pubmed.ncbi.nlm.nih.gov/42724435/). JFMS open reports, 2026. 9. [Intracranial abscess and otitis interna treated by temporal burr-hole craniotomy and ventral bulla osteotomy in a Maine coon cat](https://pubmed.ncbi.nlm.nih.gov/42544215/). The Canadian veterinary journal = La revue veterinaire canadienne, 2026. ## Further Reading - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)